In present times, when energy conservation is so important, there is a serious demand for refrigerant motor-compressor units which have an output which can be varied in accordance with demand. To this end, many different systems have been proposed. One such system involves the unloading of one or more cylinders in a multi-cylinder compressor, or the varying of re-expansion volume, for the purpose of varying output. Such systems tend to be relatively complex and the efficiency in the unloaded state is not optimum. Variable speed compressors have also been used, but they require expensive controls and also the speed control and motor-compressor efficiency present some short fall at least in a reduced output condition. Systems have also been employed incorporating, in place of a single compressor large enough to carry the maximum load, a plurality of smaller motor-compressors having a combined output equal to the required maximum, with means for controlling the total system in such manner as to selectively activate and deactivate less than all the compressors when it is desired to vary the output. Such systems have good efficiency but require complex hook-up plumbing, including means for dealing with lubricating oil management to assure that all the oil remains equally distributed between each of the compressors. Incorporation of a plurality of such smaller units in a single hermetic housing has also been proposed. For example, see assignees' U.S. Pat. Nos. 4,105,374 and 4,396,360. Such units, however, incorporated relatively complex and potentially troublesome spring suspensions, and also tended to be noisier than is now acceptable.
The present invention obviates the disadvantages of the aforementioned prior systems. In accordance with the present invention, a plurality of highly efficient motor-compressor units of the welded hermetic type, which are produced in large volume on automated production lines, are employed with a minimum amount of modification, arranged in the normal vertical position and relatively close together. A single sheet metal shell is fitted closely around all of the motor-compressors to maximize the compactness of the system and provide a common oil sump for equal oil distribution, a common suction gas inlet and a common discharge gas outlet. Noise and vibration are attenuated without the need for potentially troublesome and expensive spring suspensions. There are a number of different embodiments of the invention, each one having one or more improved features.
These and other features of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings.